1. Field of the Invention
The present invention is in the field of polymer interlayers and multiple layer glass panels comprising polymer interlayers, and, more specifically, the present invention is in the field of polymer interlayers comprising multiple thermoplastic polymer layers.
2. Description of the Related Art
Poly(vinyl butyral) (PVB) is commonly used in the manufacture of polymer layers that can be used as interlayers in light-transmitting laminates such as safety glass or polymeric laminates. Safety glass often refers to a transparent laminate comprising a poly(vinyl butyral) layer disposed between two sheets of glass. Safety glass often is used to provide a transparent barrier in architectural and automotive openings. Its main function is to absorb energy, such as that caused by a blow from an object, without allowing penetration through the opening or the dispersion of shards of glass, thus minimizing damage or injury to the objects or persons within an enclosed area. Safety glass also can be used to provide other beneficial effects, such as to attenuate acoustic noise, reduce UV and/or IR light transmission, and/or enhance the appearance and aesthetic appeal of window openings.
The thermoplastic polymer found in safety glass can consist of a single layer of a thermoplastic polymer, such as poly(vinyl butyral), that has had one or more physical characteristics modified in order to, for example, reduce the percentage transmission of sound through the glass. Conventional attempts at such acoustic dampening have included using thermoplastic polymers with low glass transition temperatures. Other attempts have included using two adjacent layers of thermoplastic polymer wherein the layers have dissimilar characteristics (see, for example U.S. Pat. Nos. 5,340,654 and 5,190,826, and U.S. Patent Application 2003/0139520 Al).
A particular problem encountered with multiple layer interlayers arises at the lamination stage of processing. While single layer interlayers have conventionally been embossed with rollers to impart a texture that facilitates deairing, three layer interlayers having a relatively soft inner layer between two relatively stiffer layers, such as is found in some acoustic interlayers, will develop optical distortion if embossing of the outer surfaces of the interlayer is transferred to the inner, softer layer. European application EP 0 710 545 Al details this problem, and cautions against embossing too deeply on the outer layers of a three layer interlayer.
Further compositions and methods are needed to improve multiple layer interlayers and the multiple layer glazing panels in which they are used, and, specifically, in multiple layer glass panels comprising poly(vinyl butyral) layers, without negatively impacting optical quality.